Dineen joined the senior squad on a development contract for season 2011/12 moving to a full contract for the 2012/13 season.

Involved with the Munster Sub Academy in summer 2010, he secured a short term training contract early in the 2010/11 season after impressing in Munster A Interpro games against Leinster and Ulster, and in the British & Irish Cup game against Llanelli.

He made his league debut coming on as a 70th minute replacement against Benetton Treviso, and a week later started against Ulster in Ravenhill, scoring his first league try to clinch victory.

Dineen was one of three additional players added to the Heineken Cup squad in March 2013.

Made a strong start to the 2013/14 season scoring a try in the first game of the league campaign against Edinburgh.

Dineen scored his third Munster try - his second at Ravenhill against Ulster - in the first game of 2014 that ended in a 29-19 defeat. Sprained his ankle badly playing for Munster A against Nottingham the following week, an injury that kept him out until February.

During the 2014/15 season he made an impressive European debut when coming off the bench against Sale Sharks in round 6 of the Champions Cup in January in Thomond Park.

Injuries limited Dineen to just two further appearances that season and he left the province in the summer of 2015 having made 34 appearances for the senior team.